The present invention relates to a system for landing power on a backplane.
A backplane typically comprises a plurality of conductive layers held rigidly in spaced parallel relation by an interleaved plurality of dielectric layers. While a given dielectric layer has equal significance with respect to the two conductive layers flanking it, one sometimes finds it convenient to conceptualize the backplane as comprising a plurality of coextensive circuit board layers laminated to one another, each layer being of composite construction, including a conductive layer and a dielectric layer. The backplane carries a plurality of parallel multiterminal sockets that receive circuit packs on which the computer system components are constructed. Some of the backplane conductive layers are used for signal propagation, and comprise a relatively large number of separate conductive traces running between the parallel transverse sockets. Others of the conductive layers are so called power planes that provide the fixed voltage levels necessary for system operation, and are generally in the form of solid sheets of conductive material, typically copper.
Each socket includes a large plurality of pins known as load pins that pass through small plated holes bored through all the layers and make electrical contact with a desired one of the backplane conductive layers. Where connection to a given layer is not required, a region surrounding the hole through that particular conductive layer is insulated to prevent the pin from making contact. The plated holes are sized relative to the connector pins for a press fit.
When supplying power to backplanes one common method consists of power supply connections known as source pins that are made in a similar manner to the aforementioned load pins, but on a larger scale. It will be appreciated that current is supplied to or drawn from the power plane over a relatively small area, leading to relatively large local current densities and an unequal distribution of current over the entirety of the power planes. It will also be appreciated that due to design constrains the source pins are not always centered between the load pins, leading to unequal distribution of current over the power planes and unequal current sharing among the load pins. This power distribution system tends to be unsuitable for larger currents because load pins having a shorter linear distance to the source pins will have a lower resistance with respect to the source pins and thus will source more current than load pins further from the source pins. To avoid exceeding the current rating of the load pins closest to the power source, smaller power levels are required. This results in inefficient use of the current sourcing capacity of the distant load pins.
Power units also require guidance and backplane power connectors have traditionally been guided with alignment pins fastened to the backplane. As well, power units need to be firmly attached to the backplane requiring many mounting fasteners screwed to the backplane. The totality of these connectors consumes valuable backplate real estate, limiting the space available for power tracks of appropriate width.
An attempt to equally distribute current has been made using a stepped backplane configuration. In a stepped backplane, the conductive and dielectric layers are laminated while having the same transverse extent. An edge of the backplane is then milled to expose the conductive layers in a stepped fashion. Rectangular bus bars are then mounted to the exposed conductive layers to provide a parallel power distribution. The stepped backplane however fails to provide equal current over the length of the power planes and thus fails to provide equal current to each load pin. Moreover, stepped backplanes are costly as they require post lamination milling.
In the aforementioned methods separate A and B power units are required for the sockets they supply because, if one power unit were to service many different sockets, all those sockets would lose power if the power unit were to go out of service. It is preferable to use board real estate for signal connections rather than redundant sources of power. What is needed is a method of supplying power to sockets on a one to one power unit to socket ratio.
For the foregoing reasons, there exists in the industry a need for an improved system of landing power on a backplane that provides for a reduction in the amount of required backplane connections.
The present invention is directed to a backplane landing system that satisfies this need. The system is comprised of a backplane connected with at least one power input mount comprising a of conductive material that is conductively sealed to the backplane for the purpose of electromagnetic compatibility. The power input mount has compact power input modules mounted in a manner so as to be conductively sealed to the power input mount.
In a more limited aspect of the invention the power input mount is formed from extruded metal with the power input modules guided into position using slots in the power input mount that mate with protrusions in the housing of the power input module. The power input modules are fastened to holes in the power input mount with elastomeric gaskets providing a conductive seal.
In a preferred aspect of the invention the power input mount is substantially H shaped and edge-connected to the backplane.
In a preferred aspect of the invention the power input module comprises a means for filtering the power of radiated and conducted emission noise.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.